The present invention relates to the distinctive marking of the directions of travel on motoring highways, airports and other surfaces, with the aid of thin marker strips adhered to the traveling or other surfaces and embodying successive spaced wedges provided with retroreflective materials; the invention being more particularly concerned with improved marker strips for such purposes.
Because of the extremely shallow angle that is made between an automobile headlamp and the roadway it illuminates, only a very small percentage of the light is reflected back for use by the motorist. The problem is made even more severe by the fact that the road surface is usually quite flat with poor reflection characteristics, black asphalt being the worst road surface from this viewpoint. Average road surface visibility with low beams for the automobile headlamps at night is usually restricted to about 100 feet. Considerable improvement is made by painting a white stripe on the road surface; but even this, with a freshly painted line, does not extend road surface visibility much beyond a couple of hundred feet. When the road surface is wet with rain, moreover, the visibility is drastically reduced even with a freshly painted line and does not extend more than a few tens of feet. The thin film of water which covers the road and paint surface acts like a mirror which reflects nearly all of the automobile headlamps' light away from the motorist. Thus, during rainy weather at night, even though provided with a good white stripe, the road appears almost pitch black to the motorist--this being the major reason why night driving in the rain is so treacherous.
The art has concluded that the only practical way to overcome this poor visibility is by means of raised pavement markers which literally extend above the thin film of water and retroreflect light back to the motorist. While commonly used in certain regions of the nation, especially in sunny climates, they are seldom used in the snow regions because of the destructive effects of snowplows. Efforts have been made to overcome this difficulty by designing a protective framework or ramp which literally guides the snowplow blade up and over the marker with little damage; but the general inability of some of these markers to withstand the harsh treatment given by the snowplows has prevented their widespread adoption. Such special constructions, furthermore, are expensive and are therefore usually positioned quite far apart. In addition they are useful only at night when illuminated by automobile headlamps and are poorly visible, if at all, by the motoring public during daylight hours, often requiring an additional or supplemental marker in the form of a painted line or a plastic line for daytime driving guidance.
The art has struggled for years, however, with a wide assortment of raised pavement markers, of one configuration or another, for the major purpose of guiding the night-driving motorist. The majority of these devices have little if any detectability or utility during daylight hours and are thus confined to night-time conditions wherein the illumination from automobile headlamps is redirected by means of internal reflection back upon itself, thereby to be observed by the operator of the vehicle. These devices often take the form of buttons or mounds containing retroreflecting elements or surfaces. More recently, ramp-like configurations have been adopted in order to provide less hazard to the vehicles traveling over them, some devices, indeed, having special ramps, previously mentioned, to assist in guiding the blades of snowplows, hopefully without uprooting them. Such devices, as before explained, are costly and, of necessity, must be relatively widely spaced from one another along the roadway surface, resulting in the disadvantage that, under headlamp illumination at night, although bright in appearance, these devices at best present only pinpoints of light and not a continuous and highly desirable solid line, nor even a semblance of a skip line. During daylight conditions they are usually not observable at all by the motoring public at any distance.
In an effort to overcome some of the above and other disadvantages of such and related raised pavement markers, markers of relatively low profile have been proposed, such as those disclosed in U.S. Pat. Nos. 3,785,719, 4,035,059 and 4,279,471. These concepts, however, involved individual units which are still costly to manufacture and thus again must be used with relatively wide spacing between units to achieve realistic operational and cost effectiveness.
A more suitable approach for obviating these problems has resided in the use of thin flexible sheeting on which is contained a series of very low profile raised pavement markers as described, for example, in my earlier U.S. Pat. Nos. 3,920,346; 4,040,760; and 4,069,787; and in U.S. Pat. Nos. 4,145,112; 4,182,548; and 4,236,788. With the exception of the constructions of my said U.S. Pat. Nos. 4,040,760 and 4,069,787, such sheet markers are dependent upon having the main body of the marker constructed so as to be transparent to light, rendering the devices subject to serious light loss effects in use, caused by abrasion and accumulated dirt. In my said earlier constructions, embodying the use of somewhat saw-tooth successive wedges carried by a thin road-attachable strip, while quite satisfactory operation can be attained, it has been found that shadow effects when heading into the sun, and modification of results after the wedges have experienced some wear, as from extended use and/or snowplow defacement or the like, do not permit as effective marking in daylight, dusk or under other adverse conditions as may be desirable.
In the case of the successive wedges of substantially triangular shape taught in my said U.S. Pat. No. 4,040,760, for example, extended use revealed that under certain conditions of ambient daylight, the pavement marker became somewhat difficult for the motorist to observe. In particular, if the marker strip is oriented in such a way that the motorist is heading in the general direction of the sun on a cloudless day, the contrast between the marker and the road surface is so low that the marker becomes difficult to distinguish. During these conditions, the sun will cast a shadow of each wedge on the valley floor between the wedges. Those faces of the wedges observed by the motorist, furthermore, are all contained within the shadow and thus appear black, introducing great difficulty in distinguishing the marker from the dark road surface. The appearance of blackness or the poor contrast between the marker and the road surface is at a peak when the sun is at a low angle on a cloudless day.